1. Field of the Invention
The invention relates to the physical infrastructure for mounting electronic circuit boards or packs in computer or communications equipment.
2. Description of Related Art
Modem telecommunications equipment such as the telephone switch and the network router often employ multiple circuit boards or packs plugged into a backplane. The multiple circuit packs are arranged in rows and are mounted to a chassis or cabinet using a common locking system of pivoting plastic latches located on the face plate of each circuit pack.
A typical prior art locking system is illustrated in FIGS. 1A and 1B. The plastic latches are pivoted, with one end having a hook for engaging a chassis while the other end has an aperture that engages a latch locking clip mounted on the circuit board or pack. When each latch is in the open position, the aperture is released from the latch locking clip, which in turn disengages the latch from the chassis. Each latch is "closed" when the latch swings down so that the hook catches the chassis and the latch locking clip engages the aperture, securing the arm and thus the circuit pack. The user thus has a fairly easy way of inserting and removing circuit packs for the given equipment cabinet.
One drawback of the system, however, stems from an operator opening up the latches and removing the circuit pack when the circuit pack is active, because nothing in the system prevents the operator from disengaging the latch locking clip from the aperture and opening the latch while the circuit pack is active. Accidentally removing an active circuit pack from a piece of electronic equipment usually disables the equipment and in certain cases can also damage the equipment. The probability for accidental removal increases in cases where the electronic appliance has two identical circuit pack configurations, where one group of circuit packs serves as a back-up to the other. Operators may understandably remove an active circuit pack by mistake, thinking it is an inactive backup used for redundancy purposes.
The impact of accidental removals can be quite substantial, because equipment requiring redundant circuit packs tends to be of a critical nature, such as telephone switches. Accidentally removing an active circuit pack from such equipment could interrupt telephone or networking service and the equipment may not be easily reset to working order. Thus, it is important to prevent the accidental removal of circuit packs, particularly when the circuit packs are deployed redundantly.